a. Field of the Invention
The present invention relates to an improvement in a grinding wheel and, more particularly, to a grinding wheel suitable for heavy or hard grinding and a manufacturing method thereof.
b. Description of the Prior Art
A grinding wheel using so-called super hard abrasive grains such as diamond, silicon nitride or boron nitride is superior in hardness, durability and wear resistance. Such a grinding wheel is used for various types of workpieces including hard grinding workpieces such as super hard alloys, stone, concrete, glass or ceramics. This type of grinding wheel includes a metal bond grinding wheel, a resinoid bond grinding wheel, or a vitrified bond grinding wheel. This classification is based on the type of bond used for bonding abrasive grains since the performance of the resultant grinding wheel is known to vary significantly in accordance with the type and structure of bond used.
A metal bond grinding wheel is shown in FIG. 1 wherein abrasive grains 1 are held using a metal such as Ni as a bond. This grinding wheel has a strong abrasive grain retaining force, and excellent durability and wear resistance. However, this grinding wheel also has poor penetrative ability and cutting properties and forms only a small number of chip pockets which are easily loaded. In view of this problem, a grinding wheel having a relatively low abrasive grain density of about 75 is generally used. However, this grinding wheel has a low grinding efficiency and cannot provide a satisfactory performance for heavy and hard grinding.
In contrast to this, a resinoid bond grinding wheel using an organic polymeric substance as a bond is superior in the penetrative ability and cutting properties than the metal bond grinding wheel. However, the resinoid bond grinding wheel has a poor abrasive grain retaining force and is not therefore suitable for heavy and hard grinding. The same applies to a vitrified bond grinding wheel.
In view of these problems, a grinding wheel (FIG. 2) has been previously proposed by the present applicant as U.S. Ser. No. 492,826 (filed on May 9, 1983). Referring to FIG. 2, this grinding wheel has a structure wherein abrasive grains 1 are coated with electrically conductive coating films 3, and the abrasive grains 1 thus coated with the conductive films 3 are bonded with a bond 2 comprising an organic polymeric substance. Due to strong bonding strength between the films 3 and the bond 2, the retaining force of the abrasive grains 1 is improved and the abrasive grain density and grinding performance are improved over a conventional resinoid bond grinding wheel or the like. However, this grinding wheel still has a problem of wear of the bond 2, leaving room for further improvements in grinding efficiency, ground surface state and the like.